The present invention relates to an electrical contact lubricant composition designed to prevent or overcome a specific type of electrical contact failure.
Electrical contacts can fail by a number of different mechanisms but a common failure mechanism results from fretting, which is relative micro-motion vibration of the contact surfaces. The source of fretting motion comes from background mechanical, thermal or electrical disturbances. These vibration sources are almost always present in equipment that use electrical contacts. Fretting failure of an electrical contact surface can occur when the amplitude of the fretting motion is on the order of the size of the contacting surface asperities, which form the microscopic electrical contact paths at the contact surface. The asperity sizes and critical fretting amplitudes are typically on the order of 10 to 100 microns in magnitude. Fretting failure occurs when debris, either from the action of wear or from outside contamination, becomes lodged between contacting surface asperities and separates the asperities sufficiently to interrupt the flow of electric current. A contact lubricant that is effective against fretting failure must specifically treat the debris problem by keeping debris from accumulating and intruding into critical asperity contact points.
Many electrical contact lubricants have been proposed over the years, but such products are not specifically designed and tailored to inhibit or eliminate fretting failure of electrical contacts. Few, if any, of such contact lubricants have been demonstrated by extensive laboratory testing to significantly reduce fretting failure. The function of a typical lubricant, according to Webster's dictionary, is primarily to reduce friction and, to a lesser extent, to reduce heat and wear. A reduction in friction in the presence of background vibration will tend to increase the amplitude of fretting motion. An increase in fretting amplitude, with other factors held constant, has been shown experimentally to increase fretting failure. A contact lubricant designed to prevent or reduce fretting failure must focus on the elimination of debris build-up at the asperity contact points rather than on the reduction of friction. The use of almost any contact lubricant will reduce wear, and in turn, should reduce the amount of local debris produced by wear. However, debris that ultimately causes fretting failure can often result from outside sources of contamination rather than be the product of local wear. A contact lubricant that specifically addresses the reduction of elimination of fretting failure must focus primarily on the debris problem.